Antenna structure



N0V- 27, 1951 G. N. cARMlcHAEL 2,576,748

ANTENNA STRUCTURE Filed May l5, 1948 Patented Nov. 27, 1951 UNITEDSTATES PATENT OFFICE'TV ANTENNA STRUCTURE Gershom N. Carmichael,Griggsville, Ill.

Application May 15, 1948, Serial No. 27,202

14 Claims. (Cl. Z50-33) This invention relates to an antenna structure,and more particularly to improvements in a high gain antenna.

Beam antennae including a di-pole and relatively closely spacedparasitic elements are considerably more efcient than other types ofantennae, as a long line or a conventional di-pole, but have heretoforeproved to have certain disadvantages which is many cases offset theiradvantages. A conventional high gain beam antenna of the type here underdiscussion, for example, including a di-pole and two parasiticelemen/ts, has been extremely frequency sensitive, its efficiency bothfor transmission and reception falling ofi very rapidly with change offrequency. While the eiliciency of such an antenna is very much betterthan that of a conventional di-pole at the precise frequency for whichif, is designed and adjusted, the eilciency of such a high gain antennafalls on so rapidly that it is down to or below the efficiency of aconventional di-pole when about 3% off frequency. This made itspreferred frequency operating band so narrow that such an antenna couldnot properly cover a single amateur band, as the 20 meter band, andwould be completely out of 'consideration for the broad band offrequencies required in connection with frequency modulation ortelevision signals, for example. o

Another disadvantage of such a high gain beam antenna with parasiticelements, one which it had in common with a conventional di-pole, wasthe need of relatively complicated and critical impedance matchingnetworks if such an antenna, with its relatively low radiationresistance, was to be connected into a lead-in of the highly efficientspaced transmission line type.

Moreover, when such antennae were stacked in a structure comprising apair of similar portions spaced half a wave length vertically, there wasa further need for a coupling network providing proper phasing of thecurrents so that the transmission line would be operating at maximumefficiency in relation to both the upper and lower portions of theantenna structure.

I have devised and am here disclosing and claiming an antenna structurewhich overcomes these and other disadvantages of high gain antennaepreviously known, which may be directly connected in simple manner to aspaced line leadin with proper matching of radiation resistance andcurrent phases, and which has extremely high efticiency, both ontransmission and reception, over almost-l unbelievable frequency bandwidths. invention will be apparent from the following specification andthe drawings, in which:

Figure 1 is a side elevational view of a presently preferred embodimentof my antenna inventions, comprising upper and lower stacked portionseach Other features and advantages of my consisting kof an activesection and a pair of parasitic elements; Figure 2 is a view at rightangles to that of Figure 1, along the line 2-2 of that figure; Figure 3is a plan view of the upper` portion of the antenna; Figure 4 is anenlarged end view of one of the active sections as shown in Figure 1;Figure 5 is an end elevational view of another form of active section;and Figure A6 is a similar view of still another modification.

While my improved antenna is very eilicient for transmission, and hasbeen used for that pur; pose with great success, it realizes itsadvantages to the fullest in the reception of wide band signals such asthose of television or frequency mod-'- ulation, particularly at pointsbeyond what is con.- sidered the satisfactory service area for such sig;nals. While such signals are normally considered as serving only a lineof sight area, there appears to be some diffraction of these wavesorsome other phenomenon which makes weak signals available at pointsdefinitely under the horizon of the service area of such a station, as60 to 100 miles away. My antenna provides unexpectedly efficientreception of such signals and fully satis,- factory service all bui, avery few per centv of the time under conditions heretofore considered soadverse as not even to warrant any attempt'to provide television or F.M. service. Moreovenit does this with such wide band characteristicsthat a single antenna will provide very satisfactory opgeration on allthe channels of one television band, for example, and where conditionsare not too ad.- verse will extend this satisfactory coverage alsothrough the frequency modulation band and possibly even on down into thelower television band, rather than requiring a multiplicity of antennaefor satisfactory coverage of various channels and bands. A lead-in ofthe spaced parallel line type provides a very efficient energytransmission medium between an antenna and the radio apparatus, but itmust normally work into a resistance, at the antenna end, of the orderof 300-400 ohmsto achieve its efficiency. Present television receivers,for example, have adopted a 300 ohm input as a standard, so that asimilar resistance would have to exist at the antenna end of thetransmission line. I have found that by making my active or centersection of the high gain antenna, the one to which the lead-inconnection is made, cagelike in character, with the di-pole an interiorelement in a cage including surrounding rod-like elements connected attheir ends to the di-pole, an unexpectedly high radiation resistance andoperating efficiency are obtained which are very much greater thantheory would indicate from mere multiplication of a folded doublet, forex' ample. An antenna having two parasitic elements and a cage-likeactive element comprising a central di-pole and live rod-like elementssym' metrically spaced therearound and connected thereto at the ends,with all of said elements `be` 2,576,748 if i?? ing parallel and havinga length slightly less than that of a half wave of a frequency at thecenter of the band in which the antenna is designed tbo'perate';provides not' onlythe extremely high gain operational eihciency- I havementioned, but also a radiation resistance of about 300 ohms,

so that a spaced parallel line transmission li'ne':v

may be used to directly connect such activesec tion to the input of thetelevision receiver,`for example. cageelements very greatly increases`the tradiation resistance, the addition of one more exterior element,in a high gain antenna havingftwo-parasitic elements in addition to thecage-like active section increasing the radiationresistance from theorder of! 300` ohmstoupver-y nearly to 500 ohms.

When Ispeak oi"` radiationgresistance. throughoutthisrrspecification-,r/it is to be understood that I- aml speaking of`the eiectiveresistance oft-the antenna, whether it beused fortransmission or reception. While the term radiation .resistance isVnormally associated w-itha characteristeofthev antenna duringtransmissionI am hereusingthe term asa measurecf thefeieetive or workingresistance of the antenna,A whether it s-beingf used for transmission Yor reception.

L have*- also' found that, where. identica-luantennastructuresarestacked a half ,wavef length apartf a simpleY spaced line connection'may'xbe usedtherebetween', and: as a lead-ingrif ther con'-Vnectionbetween' ther two portions" of theI stacked antenna is`rever-"sedY or crossed near" one ofi the portions;A as thelow'erportion. and the lead-in connection' isV made tothe' itu-,ormedia't'eVconnection'a't ay point above thi's'c'ro'ss-over and' where the'currl'e'nts'` haveth'eir maximumfadditive effect: that is, are in'phase. Wave propagation o'f thekindf of which I' anr speaking, in` atransmission' line" ribbon with'a plastic dielectric, as used televisionand.' F. has a speedofthe order of 82% of*V the velocity of radio waves'in free space, and I have found that ata pointl half wayv between the82% point and the' closer" an"- tena portion (that is, about.9% ofthe'distance from" such antenna portion), the maximum additive effectmay be obtained. While other factors' provide some slight variationswhichk may reduire very minor adjustment of the spacing Vo'f this point,having the lead-in connection: half of the distance from one portion. ofa' stacked antenna', as the lower portion, vand `.the point which is thesame percentage ofA distance-from rangement with a simple parallel. lineconnection therebetween and with a parallel line lead-in or transmissionline Awith'notv only proper impedr-v ance lmatching but also withcomplete elimination` of :any necessity for phasing networks.v v

Referring now to the particular embodiment ofmy invention illustrated inFigures 1 to` i of the drawings, the antenna structure is-shownascomprising identical upper and` lower stacked portions having Ythecenters of their conductive antenna elements spaced half a wave length.The `two portions are shown as supported by; a post l0, which may berotatable about its'axis andA controlled in anyV conventional manner vtovary thedirectionof vthe axis of best propaga--` tion- ,andf 4reception(hereinafter termed theY beam axisllif desired: Since the upper andlowerpor-,f '1Q tions are identical only the upper portion will bedescribed in detail.

The post lll carries at the top thereof a crossbai" I lf carryihgtwosupporting Aor, frame members illustrated' as pipes l2 and I3,`extending parallel to the beam axis. At the front and back of theantenna, speaking in terms of the beam axisare.a pair of continuous orunbroken rodlike elements I4 and I5 supported at an appro- The additionof furtherfexterion or? 10i .priateb'distance-above the supportingframe-work by pairs of insulators, as for example rods I6 and' Il' ofLucite. The two rod-like elements lll-.and 'I5 are conductive, as forexample being copper rods or tubes 5/8' of an inch in diameter(althoughV wire is satisfactory,- andi-intended to beincludedalso-by theterm frod-like," element-s. and comprise the parasitic elementsofya@4high gain antenna withftwosuchelements; Theffor- WardI element 1.4-,normally termed Ythe director in. transmission! andA collector ,inreception, should. be slightly less thancha-lf.' a wave length inIengthVas for Vexample V.96. of; a halff'wavc length., spaced.. aysmall. fraction of. `awave-'length from` the activeI section of. the.antenna. .being spaced ofA awaVe-length in the antenna illus.- trated.;yThe other. elementzl5 comprises a Vsirnilar. continuous conductiveiod.nor tube, and should have a length slightlygreater. than ahalf wavellength, as for exam-ple,4 1.05.- times, a-fhalf wave length,v and'A istpreferably ,spaced slightly farther than. the otherI element as'fort-example .l5r wave length-from' the center of the active section Itwilllbetunderstocd that when a-wave length is spoken of, ityis-.thewai/er leng th-.of.r a frequency at or nearthemiddleoiirthe-.band of frequencies 'which the antenna iszdesigned'l@cover., vSince the-fantennafhasvery wideband characteristicsfthelengthsare. not critical;-but best: results areobtained for a givenwavelengthat, or preferably 'slightly below thevcenter'frequency. of theband' -to'be-covered-.; fact,.;the lack offrequency `sensitivity` issuchnthatcthe parts may be cut to length by formula, withu absolutely 1noneedof -themechanicalfadjustments of elementy length nowconsidered'necessary-A in connection .with `high gain antennae of'conventional type. -i

The: intermediate or-vactive section of vtheauten-na,l in the sensethat-it iszthe section toV which currents are conductively deliveredduring transmission and from whicn'they areconductively led duringreception,v isa cage-like device; identiied in general ras A. Itis?shown as comprising.V a central di-poleconsisting of thesymmetricalrod-likefparts- I8at and Ib, separated at. the center by asmallf'spacing, as for example two inches. WhileA thisy space. isshownfopenin the drawings; forclarity' of illustrationfit woulcixin practicenormallybemechanically closed by insulating material, as ashort rodi ofLuciter.to provide a single mechanical entity; The entire cage-likeactieve section is preferably supported from the supporting frame, asbya transverse member I9: and insulating. rods#y Zik-2t, 22 and 23; withthe center ofthe diepole element in the same plane asA the-elements I4and'l;

Surrounding the di-'pole areI aplurality of symmetrically spaced.continuous .rod-like elements forming the exterior elements ofthecagelike section, 'thesebeinghere identified as 24; E5', 2B, 2,28.a'nda29; They 'are connected tothe Vdi-pole-at each endconductively,iasfby the transspaced more than the diameter of either,but 4I prefer to have the di-pole somewhat larger than the exteriorelements. Moreover, the spacing between the interior and exteriorelements, while it should be greater than the diameter of either, ispreferably only a very small fraction of the wave length for which theantenna is being designed, as for example 21/2 to 5%. 'Ihe length of thecage-like element (that is, of all of the parallel components thereof)should preferably be equal to a half wave length less twice the diameterof the cage.

While the exterior elements of the cage shown in Figures 1 to 4 are sixin number, this results in a slightly higher radiation resistance thandescribed for best reception of television, for example, where suchresistance should be of the order of 300 ohms. In Ian antenna of thecharacter described I find that this value of radiation resistance canbe achieved by using ve symmetrically spaced exterior elements, and insuch case I may provide an end structure for the cage of the charactershown in Figure 5. Here the central element or di-pole 50 has at eachend thereof a ve-armed metal plate 5| carrying the exterior rod-likeelements 52, 53, 54, 55 and 56. By having the interior element a di-poleand the exterior elements continuous, with connections at the ends ofthe cage-like device, some phenomenon occurs which I cannot at presentfully explain in theory, but which results in an unexpectedly highradiation resistance of an antenna including this section when there aresufficient exterior elements, in more than one plane, to provide a cageeffect, and which results in more efficient transmission and receptionof energy than would be the case from merely increasing the effectivesurface. The conductive and inductive currents set up in the variouselements of the cage bear such phase relationships that the radiationresistance rises as the square of the total number of elements(including the interior element) in this section. That is, instead ofthe radiation resistance of a cage-like section with six exteriorelements being only about 18%% greater than one with five exteriorelements, as would be indicated by conventional folded doublet theory,such an arrangement actually provides in the order of 45% higherradiation resistance. In addition, the radiation and receptionefficiency is not only very much greater at the wave length for whichthe antenna is designed, but is still greater, at as much as an octavehigher frequency, than that of the conventional oli-pole designed forsuch higher frequency. j The spacing between the two sections of thedipole at the center, shown somewhatlarger than actual in the drawingsfor purposes of clarity, is very satisfactoryv when in the neighborhoodof two inches, the inner ends of the di-pole sections then connectingdirectly to the leads of a spaced parallel line transmissiontape of thekind found so satisfactory for television, these Y leads being hereidentified as 33 and34. Referring particularly to Figure 2, it will benoted that these's'ame leads 33 and 34connected to the inner ends of thetwo sections ofthe di-pole of the lower portion of the stacked antennastructure, but in reversed relationship, crossing quite close to thelower antenna. With a propagation velocity in the lead-in of the orderof 82% of that in free space, as mentioned heretofore, the lead-intransmission line comprising the two par- 'allelspaced conductors 35 and36 is preferably' connected at a point about 9% ofthe distance betweenthe antenna portions, speaking of the center line of the conductors. Ator ,very close to this point the maximum additive effectsof the currentsfrom the upper and lower antenna portions are obtained, with maximumenergy through the lead-in to the receiver, speaking in terms ofreception, Moreover, this point provides, during transmission, theoptimum arrangement such that allphasing networks are eliminated. Itwill thus be noted that I have designed an antenna structure which notonly has high gain and extremely advantageous Wide band characteristics,but which also completely eliminates any necessity for impedancematching or phasing networks in the connection to the radio apparatus.

It will be understood that, where high radiation resistance isdesirable, additional numbers of exterior cage elements may be used.Moreover, the connections between the elements at the end of thecage-like device do not appear to be critical so long as the elementsare all connected to each other. For example, in the form shown inFigure 6, one di-pole section 66 has at one end thereof a conductive rod6I carrying a circular end connector 62 on which are mounted theexterior cage elements 63, 64, 65, 66, 61 and 63. My inventions havebeen embodied in experimental antennae with cage-like sections having upto as many as ten exterior elements, and in antenna arrangementsincluding three parasitic .elements instead of the two illustrated,proving advantageous in all such cases. It is also to be understood thatthe advantages of a cagelike active section may be obtained inconnection with any type of antenna where increase in radiationresistance, for example, is desired, as a long line antenna with thecage-like section as the active or driving section.

While I have shown and described certain embodiments of my invention, itis to be understood that it is capable of many modifications. Changes,therefore, in the construction and ar- I rangement may be made withoutdeparting from the spirit and scope of the invention as disclosed in theappended claims.

I claim:

l. A radio antenna having a single cage-like active section comprisingan interior rod-like electrically active antenna element and a pluralityof exterior rod-like elements disposed to encase said interior elementand lying in more than one plane and connected at their ends to saidinterior element.

2. A radio antenna having a cage-like active section comprising aninterior rod-like electrically active antenna element and a plurality ofexterior rod-like elements lying in more than one plane and connectedlat their ends to said interior element, said exterior elements beingparallel and symmetrically encasing said interior element and beingmechanically and electrically continuous over the whole length of theantenna.

3. A radio antenna having a cage-like active section comprising aninterior rod-like electrically active antenna element havingelectrically spaced portions, and a plurality of exterior rodlikeelements disposed to surround said interior element and lying in morethan one plane and connected at their ends to said interior element, allof said elements having a length slightly less than half the wave lengthof a frequency near the center of the band `for which said antenna isdesigned. A f ,i

7 4. PAfradio 'gantennaliaving a cage-likeactive sectionjcomprisingyaninterior di-pole'and a plu- Vrality'"orig-:xterior rod-like elementslying'in'mcre Vthan nne planenandrconnectedat their ends to havingelectrically spaced portions, yand at least five'electricallyandmechanically continuous exterior rod-like elements lying in more thanone planev and connected atthe'ir ends to opposite ends said di-pole.

6..A Afradioantennahaving a cage-like active section comprising aninterior rod-like electrically active antenna element adapted to beconnectedto an external circuit intermediate its ends andaplurality ofexterior rod-like elements lying in incre than one plane land connectedat their ends ,to said interior element, .said 'exterior ,elementssymmetrically lsurrounding s-aid interior element. and all of said,elements being parallel and .having a length slightly less than half the.wave length of a frequency near the centerof the band forwhich saidantenna is designed.

' '75A radio antenna having .a cage-like active section comprising aninterior di-pole and a plum ralitypf exterior rod-lik'eelements lying inincre than one` plane and connected at their endsto said di-pole, saidVexterior elements symmetrically surrounding said dij-pole. and saiddi-pole and elements being vparallelanl having a lengthslightly lessthan half the wave length ,of a frequency near the. center of the bandfor which said antenna is designed,.said exterior elements beingcontinuous throughout the entire length of said cli-pole.

8. A radio antenna having a cage-like active section comprising aninterior krod-like element having electrically spacedportions, and aplurality of exterior rod-like elements lying in more than one plane andconnected at their ends to said interior element, said exterior elementsbeing spaced thr'oughout their length from said interior element morethan the diameter of said interior element and being mechanically andelectrically continuous over the whole length of both spaced portions ofsaid interior element and being dis'- posed to encase said interiorelement.

9. A-radio antennahaving a cage-like active section comprising aninterior rod-like dipole element having electrically spaced portions andbeing adapted to be connected to an external circuit intermediate itsends, and a plurality of exterior rod-like elements symmetricallysurrounding said interior element and lying in more than one planeVandconnected at their endsV to said interior element,V all 'of saidelements having al length vslightly less than half the Wave length o'f afrequency near the center of the Y band for which said antenna visdesigned, said exterior elements being spaced throughout their lengthfrom said interior element more than the diameter of said interiorelement but only a very smallV fraction of said wavelength.

10. A directional antenna having a cage-like active section andat leastone parasitic section.V said active section comprising an interior rodlike element having electrically spaced portions and a plurality ofelectrically continuous exterior rod-like elements symmetricallysurrounding said interior element and lying in more. .than one plane andconnected at their ends to said interior .ele-

Anien't,"al1cfisaid elements having a length slightly 'less than `halfthe :wave 'lengthl of a frequency nearthe :center of the band'forwhich'said antenna is designed.

.11..A1directional antenna having -a cage-like active section and atleast oneparasitic section, said active section comprising an interiorrod-like di-pole element and a plurality of electrically continuousexterior vrod-like elements lying in more than 'one plane and connectedat their ends to said interior elementadjacent its ends,V said exteriorelements symmetrically surrounding said interior element. and all ofsaid elements being parallel and having a length slightly less thanvhalf the wave length of a frequency near the center of the Abandforwhich said antenna is designed.

12. A Vdirectional antenna having a cage-like active section and atleast one parasitic section, said active section comprising an interiorrod-like di-pole element connected to an external circuitintermediateits ends `and a plurality of electrically continuousexterior rod-likeelements .surrounding said di-pole and lying in morethan one plane and connectedat their ends to said interior element atthev ends thereof, all of said elements having a length slightly lessthanhalf the wave length of a, .frequency near the center ofthe bandffor which 'said antennais designed, said .exteriorv elements beingspaced 'from said interior element morethan'the diameter 'of saidinterior elementbut only a very small fraction of said wave length.V ,Yf

13. A directiona1 antenna structure `ccinprlsinga pair of similaryportions spaced half arwave length apart, each portion having jacagelike active section and at least fone, parasitic section, each.active section comprising an interior rodlike element and a pluralityof exterior rodlike elements lying in more thanoneplane and connected atYtheir ends to said interiorfelement, said exterior elements beingsymmetrically spaced `about said interior velement and Vall of saidelements being` parallel and having a length slightly less than half thewave length oi a frequency near 'theeenter of the band f orwhich saidantenna is designed, said interior elementbeing a di-pcle and saidexterior elements being continuous, a reversed connection between saidactive sections, Iand a lead-in Vattached to said'connection at a pointwhere the currents are additive.

1 4. Apparatus of thecharacter claimed in y'claim Vlgywherein eachdi-pol e' has` electrically spaced portions andthe reversed `connectionis between the di`polesintermediate their ends, and

Vwherein said intermediate connection is provided by a parallel wiretransmission line having a propagation velocity factorgof substantially32% of thatin free space, and-wherein saidv peint is substantially 9% ofthe distance from one dilp'ole.

' GERSHOM N. CARMICHAEL.

REFERENCES 'CITED v,The following references are of record in thefilepoi this patent:

UNITED STATESPATENTS

